1. Field of the Invention
This invention relates to a plasma display panel, and more particularly to a plasma display panel that can be driven by an active matrix system with an analog image signal. The present invention also is directed to a method and apparatus for driving the PDP.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Such a PDP typically includes a surface-discharge and alternating current (AC) type PDP that has three electrodes as shown in FIG. 1 and is driven with an alternating current voltage.
FIG. 1 is a perspective view of a discharge cell of a conventional three-electrode and AC-type PDP. Referring to FIG. 1, the discharge cell includes an upper substrate 10 provided with a sustaining electrode pair 12 and 14, and a lower substrate 20 provided with an address electrode 22. The upper substrate 10 and the lower substrate 20 are spaced, in parallel to each other, with having a barrier rib 26 therebetween. A mixture gas such as Nexe2x80x94Xe or Hexe2x80x94Xe, etc. is injected into a discharge space defined by the upper substrate 10 and the lower substrate 20 and the barrier rib 26. Any one electrode 12 of the sustaining electrode pair 12 and 14 is used as a scanning/sustaining electrode that responds to a scanning pulse applied in the address interval to cause an opposite discharge along with the address electrode 22, and responds to a sustaining pulse applied in the sustaining interval to cause a surface discharge along with the adjacent sustaining electrode 14. The sustaining electrodes 14 adjacent to the sustaining electrode 12 used as the scanning/sustaining electrode are used as a common sustaining electrode to which a sustaining pulse is applied commonly. On an upper substrate 10 provided with the sustaining electrode pair 12 and 14, an upper dielectric layer 16 and a protective film 18 are disposed. The upper dielectric layer 16 is responsible for limiting a plasma discharge current as well as accumulating a wall charge during the discharge. The protective film 18 prevents a damage of the upper dielectric layer 16 caused by a sputtering generated during the plasma discharge and improves an emission efficiency of secondary electrons. This protective film 18 is usually made from MgO. The address electrode 22 crosses the sustaining electrode pair 12 and 14 and is supplied with a data signal for selecting cell to be displayed. A lower dielectric layer 24 is formed on the lower substrate 20 provided with the address electrode 22. The barrier ribs 26 for dividing the discharge space are extended perpendicularly on the lower dielectric layer 24. The surfaces of the lower dielectric layer 24 and the barrier rib 26 is coated with a fluorescent material 28 excited by a vacuum ultraviolet ray to generate a red, green or blue visible light.
The PDP discharge cell having the structure as described above sustains a discharge by a surface discharge between the sustaining electrode pair 12 and 14 after being selected by an opposite discharge between the address electrode 22 and the scanning/sustaining electrode 12. The fluorescent material 28 is radiated by an ultraviolet ray generated during the sustaining discharge to emit a visible light into the exterior of the cell. In this case, a discharge sustaining interval, that is, a sustaining discharge frequency of the cell is controlled to realize a gray scale required for an image display.
Such a PDP driving method typically includes a sub-field driving method in which the address interval and the discharge sustaining interval are separated. In the sub-field driving method as shown in FIG. 2, one frame is divided into n sub-fields SF1 to SFn corresponding to each bit of an n-bit image data. Each of which is again divided into a reset interval RP, an address interval AP and a discharge sustaining interval SP. The reset interval RP is an interval for initializing a discharge cell, the address interval AP is an interval for generating a selective address discharge in accordance with a logical value of a video data, and the sustaining interval SP is an interval for sustaining interval a discharge at the discharge cell 12 having generated the address discharge. The reset interval RP and the address interval AP are equally allocated in each sub-field interval. A weighting value with a ratio of 20:21:22: . . . :2nxe2x88x921 is given to the discharge sustaining interval SP to express a gray scale by a combination of the discharge sustaining intervals SP.
FIG. 3 is waveform diagrams of driving signals applied to the PDP during a certain one sub-field interval SFi. In the reset interval RP, a priming pulse Pp is applied to the common sustaining electrode. By this priming pulse Pp, a reset discharge is generated between each common sustaining electrode and each scanning/sustaining electrodes of the entire discharge cells to initialize the discharge cells. At this time, a voltage pulse lower than the priming pulse Pp is applied to the address electrode so as to prevent a discharge between the address electrode and the common sustaining electrode. By the reset discharge, a large amount of wall charges are formed at the common sustaining electrode and the scanning/sustaining electrode of each discharge cell. Subsequently, a self-erasure discharge is generated at the discharge cells by the large amount of wall charges to eliminate the wall charges and leave a small amount of charged particles. These small amount of charged particles help an address discharge in the following address interval. In the address interval AP, a scanning voltage pulse SCp is applied line-sequentially to the first to mth scanning/sustaining electrodes. At the same time, a data pulse Dp according to a logical value of a data is applied to the address electrodes. Thus, an address discharge is generated at discharge cells to which the scanning voltage pulse SCp and the data pulse Dp are simultaneously applied. Wall charges are formed at the discharge cells in which the address discharge has been generated. During this address interval, a desired constant voltage is applied to the common sustaining electrodes to prevent a discharge between each address electrode and each common sustaining electrode. In the sustaining interval SP, a sustaining pulse Sp is alternately applied to the first to mth scanning/sustaining electrodes and the common sustaining electrodes. Accordingly, a sustaining discharge is generated continuously only at the discharge cells formed with the wall charges by the address discharge to emit a visible light.
In such a sub-field driving method, the reset interval RP is set for each sub-field to initialize the discharge cells in the same state. Due to the reset interval RP, however, a spurious light-emission that does contribute to the brightness is generated at the rising and falling edges of the reset voltage pulse Pp every sub-field SF1 to SFn. A brightness of a black level rises from such a spurious emission to lower the contrast. In order to overcome this contrast deterioration, a scheme of including one reset interval per frame or a reset interval having a lower frequency than the prior art, that is, a full writing period FWP as shown in FIG. 4 has been disclosed in Japanese Laid-open Patent Gazette No. Pyung 5-313598.
In the PDP adopting the sub-field driving method, the brightness is determined by the display interval, that is, the discharge sustaining interval. Since a relatively long time is wasted due to the address interval allocated equally for each sub-field SF1 to SFn, however, a time allocated for the discharge sustaining interval determining the brightness lacks. For instance, when 480 lines are scanned by a scanning voltage pulse with a width of 3 m in the address interval of each sub-field, a time of about 1.44 ms is required. Accordingly, since a time of about 12 ms (i.e., 1.44 msxc3x978) is allocated for the total address interval when 16.7 ms is allocated for on frame display interval consisting of 8 sub-fields so as to display a 8-bit image data, a time of about 4 ms is allocated for the discharge sustaining interval except for the reset interval. As a result, the conventional PDP has a problem in that the brightness is low due to a relative lack of the discharge sustaining interval determining the brightness. Furthermore, when it is intended to implement a screen with a high resolution, a discharge sustaining interval becomes more lack due to an increase in the address interval according to an increase in the scanning lines to make the display itself impossible.
In addition, the PDP has a problem in that, since a light emitting by a discharge time modulation system is superposed to display a picture, a contour noise is generated due to a discordance between an integration direction of a light assumed in the driving method and a visual characteristic recognized by the eyes of human. The contour noise usually appears in the shape of a black stripe or a white stripe between the frames. For instance, the contour noise is generated when gray levels having a large emitting pattern difference between the frames such as 127-128, 63-64 and 31-32, etc. are displayed continuously. More specifically, if the frames corresponding to 128-127 are continuous, then a large movement of an emitting position is generated because a brightness level difference between two frame is not large, but a time difference between the emitting pattern is large. In this case, since the eyes of an observer fail to keep up with the movement of this emitting position, a bright stripe is observed between two frames under a real visual state. Even when frames corresponding to 127-128 are continuous, a black stripe is observed due to the same cause. Since the most amounts of such a contour noise is generated when an object with a human body color is moved, the contour noise is founded abundantly at a moving picture caused by a movement of a human""s face or body. Also, there is a problem in that, when a color picture is displayed, a color balance is lowered to cause a deterioration of the picture.
Accordingly, it is an object of the present invention to provide a plasma display panel (PDP) that can be driven with an active system by accumulating a voltage corresponding to an analog video signal for each discharge cell.
A further object of the present invention is to provide a PDP driving method that is capable of driving the above-mentioned PDP by an active system.
A still further object of the present invention is to provide a PDP driving method that is capable of reducing an address interval as well as enlarging a discharge sustaining interval by using a single field configuration according to an analog driving system.
A still further object of the present invention is to provide a PDP driving method that is capable of displaying many gray levels by using a plurality of sub-field configuration according to an analog driving system.
In order to achieve these and other objects of the invention, a plasma display panel according to one aspect of the present invention includes a plurality of cells driven with an analog image signal, each of which comprises a sustaining electrode pair arranged in parallel for a sustaining discharge; a charge device for charging an address voltage corresponding to the image signal to initiate the sustaining discharge along with any one electrode of the sustaining electrode pair; and a discharge space into which a discharge gas is injected to cause a gas discharge.
A method of driving a plasma display panel according to another aspect of the present invention including a plurality of cells driven with an analog image signal comprises an addressing step for charging an address voltage corresponding to the image signal into a charge device provided for each of said cells; and an automatic firing and sustaining discharge step for generating a sustaining discharge during a period proportional to an address voltage charged in the charge device.
A method of driving a plasma display panel according to still another aspect of the present invention including a plurality of cells using an analog image signal, comprises the steps of: charging the analog image signal into a charge device; generating an address voltage pulse at the different timing in accordance with a voltage charged into the charge device; and initiating and maintaining a sustaining discharge responding to the address voltage pulse.
A driving apparatus for a plasma display panel according to still another aspect of the present invention including a plurality of cells driven with an analog image signal, wherein each of the cells in the plasma display panel includes first and second sustaining electrodes, a charge device for charging an address voltage corresponding to the image signal to initiate the sustaining discharge along with any one electrode of the first and second sustaining electrodes, and a discharge space into which a discharge gas is injected to cause a gas discharge, comprises a first sustaining driver for applying a firing voltage pulse for initiating the sustaining discharge and a sustaining voltage pulse for making the sustaining discharge to the first sustaining electrode; a second sustaining driver for applying a scanning voltage pulse for a switching discharge, the firing voltage pulse and the sustaining voltage pulse to the second sustaining electrode; and an address driver for applying the address voltage pulse to an address electrode included in the charge device and for applying a specific voltage changing with the lapse of time to the address electrode when the firing voltage pulse and the sustaining electrode pulse are coupled.
A driving apparatus for a plasma display panel according to still another aspect of the present invention including a plurality of cells using an analog image signal, comprising: an address driving circuit including a charge device charging the image signal, the address driving circuit generating an address voltage pulse at a timing shifted with a voltage charged into the charge device and applying the address voltage pulse to an address electrode in each cell; and a sustain driving circuit for applying a fire voltage pulse and a sustain voltage pulse to a pair of sustain electrodes, the fire voltage pulse initiating a sustain discharge with the address voltage pulse, the sustain voltage pulse generating continuously the sustain discharge.